1. Field of the Invention
The present invention relates to a portable telephone that eliminates the deterioration of speech quality due to the influence of a human body and more particularly, to a portable telephone that suppresses effectively or cancels the change of antenna impedance caused by approach or contact of a human body to the telephone without any measure for recognizing the approach and/or contact of the body.
2. Description of the Related Art
With radio communications devices or radio transceivers such as portable telephones, to match the output impedance value of the transmission circuit with the impedance value of the antenna and to match the input impedance value of the reception circuit with the impedance value of the antenna, various impedance matching circuits having different configurations have been used. The technique that several matching circuits with different impedance values are provided in advance and one of them is selectively used according to a specific condition has been well known.
For example, the Japanese Examined Patent Publication No. 58-51453, published on Nov. 16, 1983, discloses a xe2x80x9ctransmission devicexe2x80x9d configured in such a way that the impedance value is selected so as to maximize the power efficiency according to the transmitted output. Also, the Japanese Non-Examined Patent Publication No. 5-110454, published on Apr. 30, 1993, discloses a xe2x80x9cradio communications apparatusxe2x80x9d, in which several matching circuits having different impedance values are provided in advance and one of the matching circuits is selectively used by way of a switch according to the transmitted output.
In recent years, several techniques have been developed to accomplish the impedance matching in the radio communications devices or radio transceivers of this sort while taking the influence of a human body into consideration. These techniques have the intention to cancel or suppress the influence of a human body that the approach or contact of the body to the device or transceiver induces some change of the antenna impedance value, thereby deviating the antenna characteristic from its desired one.
For example, the Japanese Non-Examined Patent Publication No. 5-113216, published on May 7, 1993, discloses a xe2x80x9cwireless remote-control devicexe2x80x9d configured in such a way that a second impedance matching circuit having a different impedance value from a first impedance matching circuit is used instead of the first impedance matching circuit within a specific time period after some kind of control operation is performed by the user or until the transmission or reception operation is finished. The impedance value is changed temporarily only when the user controls the remote-control device, because the device is affected by a human body only at that time. The remote-control device has an advantage that the means or measure for detecting and/or recognizing the body is unnecessary.
Recently, there has been the tendency that the antenna impedance value of portable telephones varies or fluctuates during the talking (i.e., calling or receiving) operation due to the influence of a human body (i.e., the user""s body). This is because the distance between the user""s temple and the antenna has been getting shorter according to the progress of miniaturization and weight reduction of portable telephones. Thus, impedance value mismatch tends to occur during the talking state, resulting in inconveniences such as talking or speech interception in low electrical field (weak radio wave) areas, or voice interruption during the talking state. To prevent such the deterioration of speech quality, various techniques have been developed.
For example, the Japanese Non-Examined Patent Publication No. 11-145852, published on May 28, 1999, discloses an xe2x80x9cantenna circuitxe2x80x9d having the following configuration. Specifically, the level of the transmission power from the antenna is detected while the level of the transmission power from the transmitter is kept constant. One of impedance matching circuits is selectively used so as to maximize the level thus detected of the transmission power from the antenna. This antenna circuit has an advantage that even if the impedance value of the antenna is changed due to the influence of a human body, an obtainable antenna gain is stable, thereby improving the speech quality.
The Japanese Non-Examined Patent Publication No. 11-136157, published on May 21, 1999, discloses a xe2x80x9cmobile radio terminal devicexe2x80x9d capable of high-quality communication. This mobile radio terminal device comprises at least one impedance matching correction circuit and a human body recognizer for recognizing the contact of a human body, in addition to impedance matching circuits. The human body recognizer recognizes whether or not a human body is contacted with the device by way of a recognition signal outputted from the recognizer. If a human body is contacted with the device, the reception signal is transmitted to the at least one impedance matching correction circuit and one of the impedance matching circuits according to the level of the reception signal.
The wireless remote-control device disclosed in the Publication No. 5-113216 has an advantage that no measure for detecting the contact of a human body is necessary and therefore, the configuration of the device can be simplified. However, the configuration that the second impedance matching circuit is used instead of the first impedance matching circuit within a specific time period after some kind of control operation is performed by the user or until the transmission or reception operation is finished is applicable only to the wireless remote-control device. Thus, this configuration cannot be applied to portable telephones.
The antenna circuit disclosed in the Publication No. 11-145852 necessitates a circuit for detecting the level of the transmission power from the antenna while the level of the transmission power from the transmitter is kept constant, and a circuit for switching the impedance matching circuits in order to maximize the level of the transmission power from the antenna. Thus, the antenna circuit has a problem that the circuit configuration is complicated and the fabrication cost is raised.
The mobile radio terminal device disclosed in the Publication No. 11-136157 necessitates the human body recognizer for recognizing the contact of a human body and a circuit for selectively transmitting the reception signal to the at least one impedance matching correction circuit and one of the impedance matching circuits after measuring the level of the reception signal. Therefore, the mobile radio terminal device has a problem that the device configuration is complicated and the fabrication cost is increased.
Accordingly, an object of the present invention is to provide a portable telephone that eliminates or suppress effectively the change of the antenna impedance due to approach or contact of a human body without any special measure for recognizing the approach or contact of a human body.
Another object of the present invention is to provide a portable telephone that ensures a desired antenna characteristic with a simple and low-cost configuration.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A portable telephone according to the present invention is comprised of;
(a) an antenna;
(b) a radio section for processing a radio-frequency reception signal received by the antenna and for processing a radio-frequency transmission signal to be transmitted and sending the radio-frequency transmission signal thus processed to the antenna;
(c) a control section for controlling the radio section; and
(d) an impedance matching subsystem for matching an impedance of the antenna with an impedance of the radio section;
the impedance matching subsystem being designed to have different impedance values;
the different impedance values of the impedance matching subsystem being switched so as to be interlocked with start and stop of a talking state of the telephone.
With the portable telephone according to the present invention, the different impedance values of the impedance matching subsystem are switched so as to be interlocked with start and stop of a talking state of the telephone. In the talking state, a user of the telephone according to the invention places the telephone itself in the vicinity of his/her ear and therefore, the antenna of the telephone is located near the user""s temple or contacted therewith. On the other hand, in the states other than the talking state (e.g., the stand-by state or data communication state), the antenna of the telephone is located apart from the user""s temple. Accordingly, whether or not the antenna of the telephone is located near the user""s temple or contacted therewith can be noticed whether or not the telephone is in the talking state.
As a consequence, by switching the different impedance values of the impedance matching subsystem so as to be interlocked with the start and stop of the talking state, the antenna impedance value can be changed according to whether or not the antenna is in the state where the antenna is located near or contacted with the user""s temple. Thus, the telephone according to the invention is able to eliminate or suppress effectively the change of the antenna impedance due to the approach or contact of a human body without any special measure for recognizing the approach or contact of a human body.
Also, since any special measure for recognizing the approach or contact of a human body is unnecessary, a desired antenna characteristic can be ensured with a simple and low-cost configuration.
In a preferred embodiment of the telephone according to the invention, the control section comprises a reception signal processing circuit. The reception signal processing circuit includes an audio-frequency signal amplifier circuit for amplifying an audio-frequency signal generated by demodulating the radio-frequency reception signal. The start and stop of the talking state is detected by detecting start and stop of operation of the audio-frequency signal amplifier circuit, thereby switching the different impedance values of the impedance matching subsystem.
The audio-frequency signal amplifier circuit enters its operating state if the radio-frequency reception signal contains audio or speech information, in other words, if the telephone is placed near the user""s ear (i.e., the telephone is located near the temple of the user or contacted therewith). On the other hand, the audio-frequency signal amplifier circuit stops its operation if the radio-frequency reception signal contains no audio or speech information, in other words, if the telephone is located apart from the temple of the user. Accordingly, whether or not the antenna of the telephone is located near the User""s temple or contacted therewith can be noticed by way of detecting whether or not the audio-frequency signal amplifier circuit is in the operation state.
As a result, by switching the different impedance values of the impedance matching subsystem so as to be interlocked with the start and stop of operation of the audio-frequency signal amplifier circuit, the antenna impedance value can be changed according to whether or not the antenna is in the talking state where the antenna is located near or contacted with the user""s temple. Thus, in the above-described preferred embodiment of the invention, the telephone is able to eliminate or suppress effectively the change of the antenna impedance value due to approach or contact of a human body without any special measure for recognizing the approach or contact of a human body.
In the above-described preferred embodiment, it is preferred that the start and stop of operation of the audio-frequency signal amplifier circuit is carried out by way of a switch that controls supply of electric power to the audio-frequency signal amplifier circuit. In this case, there is an additional advantage that the start and stop of operation of the audio-frequency signal amplifier circuit can be recognized with a simple configuration.
In another preferred embodiment of the telephone according to the invention, the impedance matching subsystem comprises impedance matching circuits having the different impedance values. The different impedance values of the impedance matching circuits are switched by selecting one of the impedance matching circuits. In this embodiment, there is an additional advantage that the impedance matching circuits can be designed to have the same configuration that produces the different impedance values.
Alternately, the impedance matching subsystem may comprise a single impedance matching circuit having the different impedance values. The different impedance values of the single impedance matching circuit are switched by selecting one of the impedance values of the single impedance matching circuit. In this embodiment, there is an additional advantage that the circuit scale of the impedance matching subsystem can be smaller than the case where the impedance matching subsystem comprises a plurality of impedance matching circuits.
In still another preferred embodiment of the telephone according to the invention, a first one of the different impedance values of the impedance matching subsystem is set at a value that optimizes impedance matching between the antenna and the radio section without taking an influence of a human body into consideration, and the first one of the different impedance values is selected when the telephone is not in the talking state. Moreover, a second one of the different impedance values of the impedance matching subsystem is set at a value that optimizes impedance matching between the antenna and the radio section with taking an influence of a human body into consideration, and the second one of the different impedance values is selected when the telephone is in the talking state. In this embodiment, there is an additional advantage that the influence of a human body to the antenna can be eliminated approximately completely.
In a further preferred embodiment of the telephone according to the invention, a return loss of the antenna seen from the radio section is minimized (i.e., the magnitude of a return loss of the antenna seen from the radio section is maximized) at a first frequency when the telephone is in the talking state and at a second frequency when the telephone is not in the talking state. The first frequency is higher than the second frequency. In this embodiment, there is an additional advantage that the advantages of the invention can be more conspicuous.
In this embodiment, it is preferred that the first frequency is changed to a frequency equal to or near the second frequency due to the influence of a human body. In this case, there is an additional advantage that the influence of a human body to the antenna can be eliminated approximately completely.
In a still further preferred embodiment of the telephone according to the invention, at least one additional antenna is further provided for diversity reception. The different impedance values of the impedance matching subsystem are switched for each of the antenna and the at least one additional antenna. In this case, there is an additional advantage that the influence of a human body to these antennas can be eliminated or effectively suppressed in the diversity reception.